1. Field of the Invention
The present invention relates to metrology for semiconductor manufacturing applications, and in particular to a method and system for adapting metrology systems to work with different metrology devices.
2. Related Art
As integrated circuits (IC""s) evolve towards smaller critical dimensions (CD""s) and faster response time, new challenges are encountered in the manufacturing processes. Accurate metrology for measurement of features with sizes on the order of 100 nm or smaller is desirable.
Optical metrology has emerged as an effective tool, with several advantages over other metrology methods such as Scanning Electron Microscopy (SEM). Optical probes are non-destructive, can be employed in production monitoring and control, and can be used for determination of thickness and topographic information as well as for CD measurement.
Known methods in scatterometry are used to reconstruct a diffraction grating profile from its optical diffraction responses, at a fixed incident angle and multiple wavelengths. A library-based methodology for profile extraction utilizes libraries of diffraction signals and simulated grating profiles which include such detailed profile characteristics as: rounding, footing, T-topping, material thickness variation, sidewall angles, and CD variation. Mask information, thin-film information such as parameters describing optical properties n and k, and thickness values, are inputs which are used to compute the diffraction signal of a collection of simulated profiles. To determine the profile of an integrated circuit structure, the diffraction signal is measured for that structure and compared with the library of simulated diffraction signals, and a best match is found, i.e., a profile whose simulated diffraction signal best matches the actual measured diffraction signal.
The diffraction signals are typically calculated by a grating response simulator which utilizes Rigorous Coupled-Wave Analysis (RCWA) analytical techniques, as described in the article xe2x80x9cSpecular Spectroscopic Scatterometryxe2x80x9d, IEEE Transactions on Semiconductor Manufacturing, Vol. 14, No. 2, May 2001, pp 97-111, by Niu et al. Other simulation algorithms may also be used to calculate the spectral scattering responses or diffraction signals. An integral method is described in xe2x80x9cNumerical Methods for the Analysis of Scattering from Nonplanar Periodic Structuresxe2x80x9d, A. R. Neureuther and K. Zaki, Int""l URSI Symposium on Electromagnetic Waves, Stresa, Italy, pp 282-285, 1969. A differential method is described in xe2x80x9cSystematic Study of Resonances Holographic Thin Film Coulersxe2x80x9d, M Neviere et al, Optics Communications, Vol. 9, No. 1, pp 48-53, September 1973.
The hardware used in conjunction with metrology, which may include a metrology beam source, ellipsometer, reflectometer, and the like, is subject to parameters, which are not exactly reproducible. Examples of hardware-related variable parameters include: angle of metrology beam incidence, numerical aperture, wavelength range, polarization, and noise. The variation in hardware causes problems relating to metrology. The library diffraction signals are calculated according to inputs based on a particular set of hardware specifications, and according to ideal material characteristics. If the actual pieces of hardware and batch of material used in the measurement of a sample""s diffraction signal have slightly different specifications or characteristics than those used in the library calculations, inaccuracies may be incurred when matching the measured diffraction signal to the calculated library diffraction signals. Typically, a library of diffraction signals and associated profile data is created for a specific metrology hardware model and other parameters. This library may not provide accurate results when used for another metrology tool even for a similar hardware device from the same manufacturer and the same model.
The present invention includes a method and system in integrated circuit metrology for adapting a metrology system to work with diverse metrology devices. The method comprises measuring a set of sites on a wafer with a first metrology device and a second metrology device, calculating differences between signals of the first set of diffraction signals and the corresponding signals of the second sets of diffraction signals and determining signal adjustment vectors. The signal adjustment vector is configured to enable metrology data created for the first metrology device to be used in a corresponding second metrology device, the metrology data may be a library of simulated diffraction signals and associated profiles. In one embodiment, identifying information about the first and the second metrology devices plus the associated signal adjustment vectors may be stored in a data store.
Another embodiment is a system for storing integrated circuit metrology signal adjustment data and responding to request for signal adaptation, the system comprising a query device configured to send a query including identifying information about a metrology device and identifying information about a library of diffraction signals and associated profiles, a signal adjustment server coupled to the query device and configured to process the query and further configured to format and transmit a response to the query device; and a data store coupled to the signal adjustment server and configured to store a signal adjustment data, identifying information about a metrology device, and identifying information about a library of diffraction signals and associated profiles.